FERMI LARGE AREA TELESCOPE DETECTION OF EXTENDED GAMMA-RAY EMISSION FROM THE RADIO GALAXY FORNAX A

• Published in: The Astrophysical journal 2016-07, Vol.826 (1), p.1-1
• Main Authors: Ackermann, M., Ajello, M., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Brandt, T. J., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Cameron, R. A., Caragiulo, M., Cavazzuti, E., Cecchi, C., Charles, E., Chekhtman, A., Cheung, C. C., Chiaro, G., Ciprini, S., Cohen, J. M., Cohen-Tanugi, J., Cutini, S., D'Ammando, F., Davis, D. S., Palma, F. de, Desiante, R., Lalla, N. Di, Mauro, M. Di, Venere, L. Di, Favuzzi, C., Fegan, S. J., Fukazawa, Y., Gargano, F., Gasparrini, D., Georganopoulos, M., Giglietto, N., Giroletti, M., Godfrey, G., Green, D., Guiriec, S., Hays, E., Hewitt, J. W., Jogler, T., Jóhannesson, G., Kensei, S., Kuss, M., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lubrano, P., Magill, J. D., Manfreda, A., Mayer, M., Mazziotta, M. N., McConville, W., McEnery, J. E., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nuss, E., Ohno, M., Ohsugi, T., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Reimer, A., Reimer, O., Schmid, J., Sgrò, C., Simone, D., Siskind, E. J., Spandre, G., Spinelli, P., Stawarz, ., Takahashi, H., Thompson, D. J., Torres, D. F., Tosti, G., Vianello, G., Wood, K. S., Zimmer, S.
• Format: Article
• Language: English
• Subjects: ASTRONOMY AND ASTROPHYSICS; Astrophysics; Cosmic microwave background; Emission; Flux; galaxies: active; galaxies: individual (Fornax A); galaxies: jets; gamma rays: galaxies; Lobes; Morphology; Physics; radiation mechanisms: non-thermal; Radio; Radio galaxies; Telescopes
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/0004-637X/826/1/1

ABSTRACT We report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to be % of the total γ-ray flux. A preferred alignment of the γ-ray elongation with the radio lobes was demonstrated by rotating the radio lobes template. We found no significant evidence for variability on ∼0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. With the extended nature of the γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ∼2-3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton-proton collisions of cosmic rays with thermal plasma within the radio lobes.